Hydraulically controlled variable stroke pump



July 17, 1956 F. D. FUNSTON 2,754,806

HYDRAULICALLY CONTROLLED VARIABLE STROKE PUMP Filed Feb. 29, 1952 TORESERVOIR 2g I 26 9 Z9 41 20 Z6 30 30 a 2/ \J 1' 4 m our 5/ I INVENTOR.F172: F. D. Funsfon AT TORNE Y United States Patent HYDRAULICALLYCONTROLLED VARIABLE STROKE PUMP Frederick D. Funston, Tujnnga, Calif.,assignor to Bendix Aviation Corporation, North Hollywood, Calif., acorporation of Delaware Application February 29, 1952, Serial No.274,138

2 Claims. (Cl. 121-41) This invention relates to a variable volume,constant pressure, piston type pumps in which the stroke of the pistonis varied in response to the output pressure.

An object of the invention is to provide a practicable and relativelyquiet pump of the type mentioned, capable of operating efficiently atrelatively high pressures.

Another object is to provide smooth and positive variation of the strokeof a high pressure piston pump in response to variation in outputpressure.

Other more specific objects and features of the invention will appearfrom the description to follow of a preferred embodiment of theinvention.

Briefly, my pump is of the piston type having a piston reciprocated by acrankshaft through an articulated connecting rod linkage whereby thestroke can be varied. The linkage is adjusted by a hydraulic motorpiston relatively powerful as compared to the stresses applied to thelinkage by the reaction of the pump piston, and the position of themotor piston is determined by a relatively small spring-biased pressureresponsive valve exposed to the output pressure of the pump.

A complete understanding of the invention may be had from the followingdetailed description with reference to the drawing, in which:

Fig. 1 is a side elevation of a 3-cylinder pump incorporating theinvention.

Fig. 2 is a vertical cross-secti0n in the plane II-II of Fig. 1.

Fig. 3 is a detail cross-section in the horizontal plane Ill-III of Fig.2 and Fig. 4 is a detail vertical cross-section corresponding to aportion of Fig. 2 but showing a different stroke adjustment.

Referring to Figs. 1 and 2, the pump therein disclosed comprises a baseformed in two sections 11 and 12 for cenvenience in manufacture andrepair. Standards 13 and 14 rising from opposite ends of the upper basesection 11 rotatably support a drive shaft 15 which is shown as having adrive gear 16 on one end. The shaft 15 carries three cranks in the formof eccentrics 17, 17a, 17b associated with the three cylinders of thepump. Three connecting rods 18, 18a, 18b are mounted on the respectiveeccentrics 17, 17a, 17b.

Referring to Fig. 2, the connecting rod 18 associated with the rightmostcylinder (taken with reference to Fig. 1) is pivotally connected by apin 19 to the upper end of a link 20 which is pivotally connected by apin 21 at its lower end to the upper end of a pump piston 22 which isreciprocable in the pump cylinder 23. The connecting rod 18 is alsopivotally connected by the pin 19 to one end of a link 24, the other endof which is pivotally connected by a pin 25 to one end of a bell cranklever 26 which is fulcrumed to a shaft 27 supported at its opposite endsin the standards 13 and 14 respectively. The outer end of the other armof the bell crank lever 26 is connected by a pin 281 to one end of alink 28, the other end of which is pivotally connected to a cross member29 which is seice cured to the upper end of a piston rod 30 which issecured at its lower end to a piston 31 which is reciprocable in acontrol cylinder 32 formed in the base 10. The opposite end of the crossmember 29 is connected to one end of a link 28a, the other end of whichis connected by a pin 271 to one arm of a second bell crank lever 26a,the other arm of which is connected to the link 24a associated with themiddle connecting rod 18a. The bell crank lever 26a is formed integrallywith a hub 301 rotatable on the shaft 27, and with an arm 26b, the outerend of which is pivotally connected to the link 24b associated with theleft connecting rod 1812.

Each of the pump cylinders 23 is provided with an inlet valve 34connecting it to an inlet manifold 35, and with an outlet valve 36connecting it to an outlet or pressure manifold 37. Each reciprocationof a pump piston delivers to the outlet manifold a volume of fluiddependent upon the stroke of the piston, and the strokes of the pistonsare automatically lengthened to increase the output when the pressure islow, and shortened to decrease the output when the output pressure ishigh. The strokes are determined by the positions of the bell cranklevers 26, which positions are in turn determined by the position of thecontrol piston 31.

Thus it will be observed from Fig. 2 that the link 24 must rotate aboutits pin 25, and that the path of movement of the pin 19 in response torotation of the eccentric 17 is an are centered at the pin 25. Thisarcuate motion of the pin 19 is transmitted by the link 20 to the pumppiston 22. When the bell crank lever 26 is in the position shown in Fig.2 the arcuate movement of the pin 19 produces movement of the pumppiston 22 through a substantial stroke. However, when the bell cranklever 26 is rocked counterclockwise into position to make the axis ofthe pin 25 coincident with the axis of the pin 21, as shown in Fig. 4,the arcuate movement of the pin 19 produces no movement of the pumppiston 22.

It will be observed that the link 24 and pin 25 constitute a guide meansguiding the pin 19 for arcuate motion about the pin 25, and they aredefined as guide means in the claims.

The position of the control piston 31 is determined by pressure fluidadmitted thereabove or therebelow from the pressure manifold 37 underthe control of a valve 40 slidable in a cylinder 41 formed in thecontrol piston rod 30. Movement of the valve 40 causes the piston 31 tomove in the same direction, and the valve is urged downward by a spring42 and upward by the fluid pressure in the fluid manifold 37.

Thus the piston 31 divides the cylinder 32 into an upper chamber 32a anda lower chamber 32b. The upper chamber 32a is connected to ports 43 inthe valve cylinder 41, and the lower chamber 32b is connected to ports44 in the valve cylinder. The valve 40 has three lands 49a, 40b, and400, defining with the valve cylinder an exhaust chamber 40d and apressure chamber 40:2. The exhaust chamber 40d is always incommunication with a passage 45 in the piston rod 30 which connects tothe upper open end portion of the valve cylinder 41. The pressurechamber 40e is communicated by a passage 46 in the valve with the lowerend of the valve cylinder 41 which opens into a chamber 47 in the base10 below the cylinder 32 and separated from the cylinder by a cylinderlower end wall member 48. Chamber 47 is connected to the pressuremanifold 37 by a passage 37a so that it is filled with fluid at theoutlet pressure. This pressure acts on the lower end of the valve 40 tourge it upwardly in opposition to the constant downward force producedby the spring 42 which is compressed between the cylinder lower wallmember 48 and a disc 50 secured to an extension 40) on the lower end ofthe valve 40. A spider 40g on the extension 40) engages a stop ring 51in the piston rod 30 3 to limit downward movement of the valve withrespect to the piston rod.

The pump operates as follows. As shown in Fig. 2, the parts are in theposition they occupy when the outlet pressure in the manifold 37 and thechamber 47 is at a low value. Under these conditions, the force of thespring 42 overcomes the pressure acting on the valve 40 to urge itupwardly, and the valve occupies its lowermost position with respect tothe piston rod 30, in which the spider 40g rests on the retaining ring51. The spider and retaining ring therefore transmit the force of thespring 42 to the piston rod 30 which moves into its lowermost positionin which the control piston 31 is in the lower end of its stroke. Atthis time the chamber 32b below the control piston 31 is connected bythe port 44, the valve chamber 40d, and the passage 45, to the openupper end of the valve cylinder 41. At the same time the upper chamber32:: of the control cylinder is connected through the port 43, the valvechamber 40e, and the valve passage 46 to the chamber 47 so that Whateverpressure exists in the chamber 47 is acting against the upper face ofthe piston 31 to hold it down, in aiding relation to the force of thespring 42. The pressure in the chamber 4'7 acts always against the lowerend of the piston rod 30 to urge 1t upwardly, but the effective area ofthis rod is less than the area of the upper surface of the piston 31, sothat the pressure in chamber 32 overcomes the effect of the pressure inchamber 47 on the piston and piston rod assembly.

Under the conditions described, the bell crank lever 26 holds thelinkage connecting the eccentric 13 to the pump piston 22 in positionfor maximum stroke, so that the pump delivers its maximum capacity intothe outlet manifold 37. When the pressure in the outlet manifold 37rises to a predetermined value, this same pressure in the chamber 47becomes efiective to urge the control valve 40 upwardly and compress thespring 42. Upward movement of the valve carries the land 40b thereonacross the port 43 to cut off the connection of pressure fluid to theupper chamber 32a and block this chamber so that the piston 31 is lockedin position. At the same time, the land 40a on the valve blocks the port44 to block flow of fluid into or out of the lower chamber 3%. A furtherincrease in pressure raises the valve 40 until the land 4011 clears theport 43, and the land 40a clears the port 44. This permits fluid todischarge from the port 43 into the low pressure valve chamber 400., andadmits fluid from the chamber 47 through the lower end of the valvecylinder 1 into the port 44. The pressure in the lower pump chamber 32bis sufficient to elevate the control piston 31, thereby shifting thelinkage to reduce the stroke of the pump piston 22. As the pressurecontinues to increase, the stroke of the pump is reduced until itfinally reaches Zero value, when the axis of the pin 25 is coincidentwith the axis of the pin 21.

it will be observed that the piston 31 has a follow-up action withrespect to the valve 40. Thus as soon as the piston 31 rises in responseto an upward movement of the valve 40 to carry the land 40b above theport 43, the piston then rises relative to the valve and cuts otl theport. The reverse action takes place when the pressure is falling andthe valve 40 moves downward in response thereto.

An important feature of the invention is that whenever the follow-upmovement of the piston 31 closes the ports 43 and 44, the fluid in thechambers 32a and 32b is blocked from escape, thereby locking the piston31 positively in position, so that it cannot be shifted even to a slightextent by the reaction forces applied thereto from the pump linkage.This prevents the linkage from yielding with each cycle of the pumppiston 22.

The pump, as disclosed, is intended to be located in a sump or reservoirso that fluid discharged through the open upper end of the valvecylinder 41 will return to the sump. However, if some other arrangementis desired, the upper end of the passage 41 can be connected to a returnline by a flexible hose.

Although for the purpose of explaining the invention, a particularembodiment thereof has been shown and described, obvious modificationswill occur to a person skilled in the art, and I do not desire to belimited to the exact details shown and described.

I claim:

1. Pressure-responsive stroke-adjusting means for a variable-stroke pumphaving a stroke-controlling element oscillatable through a fixed pathand an outlet passage, said means comprising: a hydraulic motor having amotor cylinder and a piston reciprocable therein and adapted to becoupled to said stroke-controlling element of said pump for actuatingit; valve means for said motor com prising a hollow piston rod extendingfrom said piston member through both ends of said motor cylinder anddefining a valve cylinder; a motor port in said valve cylinder extendingthrough said piston rod to said motor cylinder on one side of said motorpiston; a piston valve slidable in said valve cylinder and having landsdefining with said valve cylinder a pressure chamber and an exhaustchamber; passage means communicating said exhaust chamber with one endof said hollow piston rod constituting an exhaust duct; passage meanscommunicating said pressure chamber with the other end of said hollowpiston rod; means defining a closed chamber beyond said motor cylinderand adapted to be connected to said output passage of said pump intowhich the other end of said hollow piston rod projects, whereby the pumpoutput pressure is applicd to the other end of said valve cylinder andsaid valve piston to urge the latter toward said one end of said pistonrod; spring means urging said valve piston toward said other end of saidpiston rod; said valve cylinder port and said valve piston chambersbeing so longitudinally disposed relative to each other that in aneutral position of the valve'piston with respect to the motor pistonsaid port is intermediate said exhaust and pressure chambers defined bysaid pison valve, and movement out of said neutral position in eitherdirection connects said port to that one of said chambers to producefollowing movement of the motor piston and restore it to neutralposition with respect to said valve piston; and means for conveyingfluid to and from said motor cylinder on the other side of said motorpiston.

2. Apparatus according to claim 1 including inter-engagingstroke-limiting means on said valve piston and motor piston member,respectively, whereby said spring means is effective to move said pistonmember into position producing maximum stroke of said pump in theabsence of opposing pressure forces.

References Cited in the file of this patent UNITED STATES PATENTS1,292,457 Hall Jan. 28, 1919 1,418,952 Martin June 6, 1922 1,957,556Schelling May 8, 1934 2,044,064 Dake June 16, 1936 2,070,935 Traut Feb.16, 1937 2,303,597 Adelson Dec. 1, 1942 2,563,939 Kishline Aug. 14, 1951

